My Dyson DC01 seems to have lost suction ?

My DC01 seems to have lost suction - the beater beats and the hose sucks, but there seems to be little suction to lift dust via the
beater. I have replaced filters and cleaned fluff from the beater chamber and the rubber flaps all seem to seat OK, but all to no avail? Any ideas? Could the seals on all the moving lumps of plastic be at fault?